1. Field of Invention
This invention pertains to a coating composition and a process for coating a porous, substantially glass fiber mat so that the resultant mat can be used as a water resistant underlayment material for the construction industry.
2. Prior Art and Other Considerations
Many forms of weather resistant webbed sheets have been developed for the construction industry as "underlayment" for installation under shingles or siding. Examples of such webbed sheets range from construction papers such as "tar paper", to spun-bonded polyolefin house wraps.
To be effectual for their purposes, the underlayment sheets must satisfy the dual criteria of: (1) maintaining dimensional stability in the varied outdoor climates of the world; and, (2) having a high degree of resistance to penetration by liquid water.
Most of the prior art construction papers have been made using a cellulosic felt or Kraft paper which has been treated with coal tar pitch, asphalt, or pine rosin. The natural tendency of cellulose to swell and expand when wet, and then shrink when dried, has presented a problem in maintaining flatness of these webbed sheets. The swelling and expansion tendencies can yield a curled, wavy, or wrinkled underlayment which is unacceptable for use with light weight siding and shingles.
In an effort to overcome dimensional instability and reduce the fire hazard, glass mats have been substituted for cellulose sheets as the base substrate. Typically, the glass mats have been saturated or coated with various asphaltic materials to reduce porosity.
One example of an asphalt binder-based coating on a glass mat is disclosed in U.S. Pat. No. 4,186,236. While useful as a foam panel facer, the mat of U.S. Pat. No. 4,186,236 did not have the necessary properties to be used as an underlayment. Moreover, the mat disclosed in U.S. Pat. No. 4,186,236 is expensive to fabricate. U.S. Pat. No. 4,186,236 requires a minimum asphalt content of 25% by weight and contends that otherwise it may be difficult to coat the glass mat. Indeed, if asphalt is used as the only binder, more than 25% by weight must be used to effect adequate adhesion.
Historically, when using latex binders as the only adhesive in aqueous coating formulations, a large cost is attendant due to high levels of latex needed. Also, the ratio of filler pigments to the dry weight of the polymer latex cannot exceed certain limits. If this ratio is too high, the pigment will no longer adhere to the substrate to which it has been applied.
In recent years, spun-bonded polyolefin house wraps have gained in popularity as a side wall underlayment. One such product is known as "TYVEK.RTM.", which is a registered trade mark of I.E. DuPont Co. The spun-bonded wraps will not curl, wrinkle, or shrink, and thus are desirable for use under light weight siding. These products, however; are limited in use as they are both expensive and present a fire hazard. They are not suitable as a shingle underlayment.
Accordingly, prior art commercially-produced mats comprise fibers (glass, cellulose, or plastic) used with a high percentage of polymer latex, or else a high percentage of asphalt, to form a water barrier as well as acting as the binder for the mineral pigment fillers. Heretofore it was thought that either latex or asphalt alone should be used as the binder material and water barrier material. Accordingly, it is an object of the present invention to provide a coating composition and method for coating a porous mat whereby the mat becomes substantially non-porous.
An advantage of the present invention is the provision of a dimensionally stable, water penetration resistant, webbed mat using less organic binder material than previously thought possible; and a process for obtaining the same.
Another advantage of the present invention is the provision of an economical and water resistant coating composition which does not get tacky when heated.
An advantage of the present invention is the provision of a novel combination of binders which provide an extraordinarily high degree of water resistance and adhesion for such a low level of hydrophobic organic materials added.
Another advantage of the present invention is the provision of a reduced porosity, predominately glass fiber mat, void of micro-fibers or fibrous glass dust, which are considered inhalation hazards.
Another advantage of the present invention is the provision of a predominately glass fiber mat which provides a safety feature of reduced combustibility.
Yet another advantage of the present invention is that the novel coating material used to lower porosity provides a mat which is smoother to the touch than a mat made of 100% glass.
A yet further advantage is that the novel binder combination and fillers provide an economical mat at the same time the porosity and the surface texture is improved.